O.R.'s Vol XVII, part 2, page 282;
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CONFIDENTIAL.] WAR DEPARTMENT,
Washington City, October 21, 1862.
Ordered, That Major-General McClernand be, and he is, directed to proceed to the States of Indiana, Illinois, and Iowa, to organize the troops remaining in those States and to be raised by volunteering or draft, and forward them with all dispatch to Memphis, Cairo, or such other points as may hereafter be designated by the general-in-chief, to the end that, when a sufficient force not required by the operations of General Grant's command shall be raised, an expedition may be organized under General McClernand's command against Vicksburg and to clear the Mississippi River and open navigation to New Orleans.
The forces so organized will remain subject to the designation of the general-in-chief, and be employed according to such exigencies as the service in his judgment may require.
EDWIN M. STANTON,
Secretary of War.
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Appearently these orders were the product of a plan put forward by McClernand to Lincoln himself. According to Catton, General-in-Chief Halleck wasn't to pleased with McClernand going over everyone heads and I can see why. The military is very touchy about staying within the system of chain of command.
I did misspeak about McClernand outranking Grant (too early in the morning to be thinking straight) Grant recieved his promotion to Major General on Februay 17th, 1862, McClernand recieved his second star on March 21st 1862. However Grant had been relieved of his command by Maj. Gen. Henry Halleck on March 2nd, 1862. But was restored to command on March 17th by Lincoln's personal intervention.
In any case McClernand took this order he recieved on October 21st, 1862 as being his ticket to an independent command away from Grant, since he (McClernand) was on the Mississppi River while Grant was advancing from Tennessee toward Oxford, Miss. Grant had given McClearnand Shermans Corp to command, seeing as McClernand was of higher rank than Sherman. McClernand saw this as his oppertunity to make a name for himself and Arkansas Post was the oppertunity for an "easy victory" to make that name.